1. Field of the Invention
This invention relates to liquid crystal displays. More particularly, it relates to preventing picture quality deterioration and shorting between adjacent pixel electrodes.
2. Description of the Related Art
A liquid crystal display (LCD) uses an electric field to control light transmittance to produce an image. An LCD includes a liquid crystal panel having a matrix of liquid crystal cells, and driving circuits for driving the liquid crystal cells. The liquid crystal panel includes a common electrode and pixel electrodes for producing electric fields in accordance with data signals. Typically, the pixel electrodes are provided on a lower substrate, whereas the common electrode is on an upper substrate. Usually, each pixel electrode is connected to a thin film transistor (TFT) that acts as a switching device.
Referring now to FIG. 1 and FIG. 2, a conventional liquid crystal display includes a lower substrate 1 having a TFT TP that is arranged at an intersection between a data line 4 and a gate line 2. A pixel electrode 22 is connected to a drain electrode 10 of the TFT. A storage capacitor SP is formed by overlapping a portion of the pixel electrode 22 and a gate line 2.
The TFT TP includes a gate electrode 6 that is connected to the gate line 2, a source electrode 8 that is connected to the data line 4, and the drain electrode 10 that is connected, via a drain contact hole 20, to the pixel electrode 22. Further, the TFT TP includes semiconductor layers 14 and 16 for defining a channel between the source electrode 8 and the drain electrode 10 when a gate voltage is applied to the gate electrode 6. Such a TFT TP responds to gate signals from the gate line 2 to selectively apply data signals from the data line 4 to the pixel electrode 22.
The pixel electrodes 22 are positioned in liquid crystal cell areas that are defined by the data lines 4 and the gate lines 2. The pixel electrodes 22 are made from a transparent conductive material having a high light transmittance. Each pixel electrode 22 forms a potential difference with a common transparent electrode (not shown) on an upper substrate. The potential differences are controlled by data signals applied via the drain contact holes 20. The potential differences cause a liquid crystal that is disposed between the lower substrate 1 and the upper substrate to rotated due to dielectric anisotropy. Thus, the liquid crystal selectively enables light from a light source to be transmitted into the upper substrate.
The storage capacitors SP restrain voltage variations on the pixel electrodes 22. Each storage capacitor SP is comprised of a gate line 2, a storage electrode 24 that overlaps the gate line 2, and a gate insulating film 12 that is disposed between the gate line 2 and the storage electrode 24. Each storage electrode 24 is electrically connected, via a storage contact hole 26 defined on a protective film 18, to a pixel electrode 22.
Hereinafter, a method of fabricating the lower substrate 1 of the liquid crystal display having the above-mentioned configuration will be described with reference to FIG. 3A through FIG. 3E. First, a gate metal layer is deposited on the lower substrate 1. That metal layer is then patterned to form the gate line 2 and the gate electrode 6.
Referring now to FIG. 3B, a gate insulating film 12 is then deposited over the lower substrate 1, over the gate line 2, and over the gate electrode 6. First and second semiconductor layers are then sequentially deposited on the gate insulating film 12. Those semiconductor layers are patterned to form an active layer 14 and an ohmic contact layer 16.
Referring now to FIG. 3C, a data metal layer is then deposited and patterned to form the storage electrode 24, the source electrode 8, and the drain electrode 10. Thereafter, as shown in FIG. 3D, a protective film 18 is deposited and patterned to define a drain contact hole 20 and a storage contact hole 26. Then, as shown in FIG. 3E, a transparent conductive material is deposited to form a pixel electrode 22 that extends into the drain contact hole 20 and into the storage contact hole 26.
In the illustrated LCD, the protective film 18 is usually made from an inorganic material having a large dielectric constant, typically silicon nitride SiNx and/or silicon oxide SiOx. Referring now back to FIG. 1, the pixel electrode 22 and the data line 4 should be separated by a certain horizontal gap x, for example, 3 to 5 μm. This minimizes coupling caused by a parasitic capacitor. However, if a misalignment occurs when forming the pixel electrode 22, the gap between the data lines 4 is not even on the left and right sides. This causes non-uniformity of the parasitic capacitances between the data lines 4 and the pixel electrodes 22. This can cause data signal deterioration, which results in degraded picture quality.
Furthermore, referring now to FIG. 4, when a transparent conductive material 22a is patterned to provide the pixel electrode 22, a portion of the transparent conductive material 22a may remain in exposed areas. Thus, there is possibility that a short-circuit may occur between adjacent pixel electrodes 22.